Slashdot videos: Now with more Slashdot!

View

Discuss

Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).

schwit1 (797399) writes with news that NASA scientists have tested the EmDrive, which claims to use quantum vacuum plasma for propulsion. Theoretically improbable, but perhaps possible after all. If it does work, it would eliminate the need for expendable fuel (just add electricity). From the article:Either the results are completely wrong, or NASA has confirmed a major breakthrough in space propulsion. A working microwave thruster would radically cut the cost of satellites and space stations and extend their working life, drive deep-space missions, and take astronauts to Mars in weeks rather than months. ... [According to the researchers] "Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma."
Skepticism is certainly warranted: NASA researchers were only able to produce about 1/1000th of the force the Chinese researchers reported. But they were careful to avoid false sensor readings, so something is going on. The paper declined to comment on what that could be, leaving the physics of the system an open problem.

No, the question is how fast can it accelerate the average potato. NASA reported 30-50 mN of thrust., call it 40. The average potato is about 375 grams, call is 400 even so math is real east. F=m*a or a = F / M or 1e-7 m/sec^2. So, accelerate for 1 year and you reach the break-neck speed of 31.5 meters per second or 70.5 mph

It is going to take a long time to get that potato to Alpha Centauri. Especially considering that you have to also accelerate the mass of the Q-drive unit itself and the energy source to

Even if the efficiency can not be improved much, the people who launch probes have impressive patience. Add a good solar panel or a nuclear source and you could get a nice constant acceleration over a long period.

No, the question is how fast can it accelerate the average potato. NASA reported 30-50 mN of thrust., call it 40. The average potato is about 375 grams, call is 400 even so math is real east. F=m*a or a = F / M or 1e-7 m/sec^2.

40 mN is 0.04N

400g is 0.4kg

a = F/m = 0.04 / 0.4 = 0.1 m/s^2 not 0.0000001 m/s^2.

Therefore accelerating for 3e7 seconds (one year) results in a velocity of 3000 km/s. About 1% of lightspeed. And a distance of 330AU. You'll hit one lightyear in 19 years. Two lightyears in about 28 years, if you turn your potato around to decelerate, you'll deliver your potato to Alpha Century in 56 years. If you want to cook your potato by skimming one of the stars, it'll only take 38 years.

Unfortunately, even though you wouldn't have to supply propellant, you would still need to supply the energy to accelerate it. After accelerating for one year, your potato's kinetic energy is 1.8e12 Joules. That's a lot of energy. Initially you can stick a solar panel on it to power the drive, but once you're out of the inner solar system that won't work any more.

Unfortunately, even though you wouldn't have to supply propellant, you would still need to supply the energy to accelerate it.

Actually you don't. Any reactionless thruster can be turned into a free energy machine. If force-produced is directly proportional to energy-input (eg, the device in TFA gets 31uN/W) regardless of position in the universe and direction of thrust (**), then the change of velocity per unit time is also proportional to energy-input. Linear. But the kinetic energy available is proportional to the square of total velocity. There's a cross over velocity where the increase in kinetic energy is greater than the ene

2. No one is claiming this device is a "free energy machine". You have to put energy in as electricity, and you don't get more energy out than you put in.

3. No one is claiming this device is "reactionless". There's ongoing discussion about the exact mechanism (assuming it actually works). They suggest it may be pushing against space itself, somewhat analogously to how a swimmer pushes against the water they're swimmi

And that's why skeptics are skeptical of the claims made for the EmDrive.

2. No one is claiming this device is a "free energy machine".

Skeptics are, because all reactionless drives are free energy machines.

You have to put energy in as electricity, and you don't get more energy out than you put in.

However, the power input is constant for the thrust out (Newtons-per-Watt), therefore power input is constant for acceleration (m/s^2-per-Watt), therefore energy input is constant for delta-V (m/s-per-Joule). But the energy out (kinetic energy) is proportional to the square of total velocity (Ek=1/2mv^2). Therefore energy-in increases more slowly than the energy-out

Skeptics are, because all reactionless drives are free energy machines.

That's doublespeak. No one who believes in it claims it's a free energy machine. Ok, you are free to announce, "It's a free energy machine, therefore it can't exist!". But since you don't have any evidence to support your claim, that's meaningless. Either it works or it doesn't. If it does work, it almost certainly is not a free energy machine. No one has presented any evidence to indicate it doesn't conserve energy. If you make that claim anyway, it just shows you're making claims that aren't based

http://steamcommunity.com/app/... [steamcommunity.com] "ishanda --- Kerbal Space Program Apr 17, 2013 @ 2:29am; If you REALLY want Star Trek Style impulse engines why not mod them yourself? All you really need is to make copies of the relevant part files, change the name of the Xenon Tank to "Deuterium" and change the Ion Engine to "Impulse Engine" and then change a few values to make them super efficient. Done."

Still looking forward to seeing how the real device pans out though... Just like I'm still wondering about all the cla

Skepticism is certainly warranted: NASA researchers were only able to produce about 1/1000th of the force the Chinese researchers reported. But they were careful to avoid false sensor readings, so something is going on. The paper declined to comment on what that could be, leaving the physics of the system an open problem.

The physics of the system has two explanations, one relativistic relying on a classical radiation pressure, and one quantum relying on virtual particles, and is not an "open problem". These are things that were designed, not things that just work but we can't explain why. The EmDrive site will give you the relativistic model; the paywalled Chinese article presumably gives the quantum model. The NASA researchers produced 1/1000th of the force of the Chinese & English drives because they used a different design, which reduces the Q factor of the waveguide - again, this is explained on the EmDrive site. Now Chinese, English and American teams have all measured "anomalous" thrusts from this type of device, so skepticism is not really warranted on that basis, nor on the basis of a presumed anomaly in thrust magnitude when in fact that's all well understood.

Unfortunately in this instance they measured the anomalous thrust on a version of the instrument designed and built by its own inventors in such a fashion as to not produce thrust at all. I'm inclined to believe that the anomalous thrust is some sort of weird ideomotor effect related to the fact that they had to manually control the frequency of the RF excitation as the test ran.

In 1989 Fleischmann and Pons published a paper showing evidence of cold fusion. No one, other than a team atmTexas AM, of course, was able to replicate. The lab where I worked had a preprint of he TAM paper andmeveryone unformly decides it was crapbduebto lack lack of experimental detailed procedure. I am told the FP paper had the same issues. Though millions was thrown t the problem in 1989 and 1990 nothing came of this discovery that gviolated all known science. Mather AM people denied fraud by claimin

Moreover, Fleischmann and Pons were getting energy out of what they were doing, so they did have experimental results. Some other people were confirming it as fusion, and were later exposed as people who had no clue how to use a neutron detector. Since then, I've been dubious about results like this (didn't stop me from trying to figure out how to put FTL neutrinos into Special Relativity, though).

We have two competing theories being advanced by people who've built this family of thruster, both of which are also widely regarded as containing flawed physics (if not necessarily well-examined), and many other provisional theories having been advanced by scientists unconvinced that the effect is real. Meanwhile, NASA tests a related apparatus and does in fact detect thrust, but of a magnitude inconsistent with the theory upon which it is constructed.

By what stretch of logic do you propose they can responsibly claim either theory is accurate? The most that they can confirm is that they did in fact measure anomalous results. Addressing the specific physics in play was far beyond the scope of the experiment they performed, and thus would be pure speculation on their part. The proper response is to do exactly what they did: not endorse any specific explanation, but confirm that a repeatable phenomena unexplained by broadly accepted physics does appear to exist. That bolsters the legitimacy of anyone exploring the phenomena without endorsing a particular theory that they lack the data to confirm (aka making a statement of "faith" or "opinion").

It's perhaps an easy mistake to make if you're not well-versed in the terminology of the field, but you are describing order-of-magnitude, a term having nothing to do with magnitude itself, which (in this context) specifies the "length" or "absolute value" of a vector value such as displacement, velocity, force, etc.

For example speed is an always-positive scalar (single-number) value that specifies the magnitude of velocity, which is a vector (multi-number) value independently specifying the speed along eac

If we have X, and something is an(one) order of magnitude bigger than X, then it is 10x bigger than X.If it is 100x bigger than X then this is two orders of magnitude and if we are talking about 1000x smaller or bigger, as in this case: it is three orders of magnitudes.

Yes. That is what an order of magnitude means. But that is not what magnitude means - it has its own definition separate from that one particular usage: size. Try reading that in the context of what I wrote:

>Meanwhile, NASA tests a related apparatus and does in fact detect thrust, but of a -magnitude-size inconsistent with the theory upon which it is constructed.

I say nothing about orders of magnitude. I only refer to the size of the effect, and note that the size is inconsistent with the theory. Th

Perhaps your interpretations have been polluted by a set of sibling posts I never saw.

But you seem to have a problem with my specific usage of magnitude, despite explanations, so I think perhaps you are being willfully obtuse, I am doing a poor job of explaining it to you, or possibly you aren't as well-versed in english technological vernacular as you think - you do imply you speak German, perhaps you are in that uncomfortable situation where the similarities with your mother tongue are just enough to occa

Ah, so we did not talk about your post but about the ACs one... so I'm not that Alzheimered as I feared.

Yes, we can agree that the word 'magnitude' has slightly different meanings, depending if other words like 'order' precede it.

Regarding english vs. german that is indeed a big problem, that is why I encourage you in any legal case regarding both languages to hire a professional interpreter (hint: the literal translation from german to english would not be interpreter but translator) e.g. words like event

Don't be deceived by vacuum chamber: the device was placed inside a chamber designed to be evacuated, but the experiments were conducted at atmospheric pressure. Ionization effects of air were not considered, and to demonstrate force at pressure and not in vacuum does nothing to establish the utility of such apparatus for extra-atmospheric purposes.

I read the actual abstract of the paper the article was based on. (the full text is not available)'The tests were performed in a vacuum chamber, with the door closed, but at atmospheric pressure.'Internal convection can move gas just fine and create anomalous torques.

Yeah, that paper should be rejected. The results are totally useless. I wonder how many people went "WTF?" upon reading "...within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure."

Fact 1: The NASA team has measured approximately 30-50 micronewtons of thrust in the experimentFact 2: The NASA team experienced a similar thrust on a test item that was NOT design to experience any force.

It is pretty obvious that there was a systematic error in NASA's experiment.

Fact 1: The NASA team has measured approximately 30-50 micronewtons of thrust in the experimentFact 2: The NASA team experienced a similar thrust on a test item that was NOT design to experience any force.

It is pretty obvious that there was a systematic error in NASA's experiment.

Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not produce thrust. Specifically, one test article contained internal physical modifications that were designed to produce thrust, while the other did not (with the latter being referred to as the “null” test article)

The big problem I have with their "test" is that they did it at atmospheric pressure. So, they're supposing the force is pushing off quantum vacuum virtual plasma. That's one possibility. The other possibility is it's pushing off THE FREAKING AIR IN THE CHAMBER.

Don't get me wrong, I would love to see a reactionless drive. A reactionless drive could get us to the stars. But it generally involves violating conservation of momentum, and that's unlikely.

Why do people always make such stupid claims:... it generally involves violating conservation of momentum, and that's unlikely. Why would a drive using microwaves to utilize a quantum effect violate impulse conservation? Your ship gets a momentum in one direction ad said quantum effect thrust holds the other half of the momentum... obviously!

If the thing works, it's not that it violates conservation of momentum, it's that it's doing something we don't understand, which appears to violate the conservation of momentum because we don't know how it works.

I'm sure many people would love to see this turn out to work because it would be a really cool real-world effect based on some of the the really bizarre and incredibly abstract physics going on these days. Like many people here I'm sure, I'm fascinated by the advances in modern physics in the last

What part of this is hard to understand? "Testing was performed on a low-thrust torsion pendulum that is capable of detecting force at a single-digit micronewton level, within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure." That's a direct quote from the abstract of the NASA paper.

1. They tested a quantum vacuum plasma thruster inside a vacuum chamber, which is probably cramped, difficult to run test instruments in, and costs more than a bench top and even closed the door but DIDN'T perform the test in an actual vacuum.

2. The did perform the test in a vacuum, but the abstract simply mischaracterizes what they did because the author of the abstract was some Public Relations flunky.

I haven't seen this vacuum issue addressed by anyone after some searching. To me it seems premature to speculate about quantum vacuum effects when interactions with air seem very likely. Perhaps they planned to perform these experiments in a vacuum, but didn't quite get to that point when the abstract was due? At this point, they may have finished the vacuum version of these experiments, so may have some results to present. If someone does know, please pitch in.

It's probably #2. The paper, as presented at the 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, is available for purchase [aiaa.org]. I happened to have a spare $25 and a burning curiosity. The full paper isn't available on the NASA site, only the abstract can be gotten there for free. If you wanna read the details, you have to pay for 'em.

Anyhow, here's the relevant bit from the paper: "Two roughing pumps provide the vacuum required to lower the environment to approximately 10 Torr in less than 30 minutes. Then, two high-speed turbo pumps are used to complete the evacuation to 5x10E-6 Torr, which requires a few additional days. During this final evacuation, a large strip heater (mounted around most of the circumference of the cylindrical chamber) is used to heat the chamber interior sufficiently to emancipate volatile substances that typically coat the chamber interior walls whenever the chamber is at ambient pressure with the chamber door open. During test run data takes at vacuum, the turbo pumps continue to run to maintain the hard vacuum environment."

I'm not a physicist, but the paper is still an absolutely fascinating read, and contains a number of color photos of the test apparatus, the device itself, etc. The amount of detail they went into for the experiment is really impressive; seismically isolating the test chamber, using liquid metal (galinstan) electrical contacts to eliminate any forces due to a mechanical coupling to a wire, compensating for the magnetic field that is created by passing electricity through the device, and so on. This is NASA we're talking about here, the guys that do ROCKET SCIENCE. The idea that they wouldn't test this device in a vacuum is laughable.

Something spooky is going on inside this device, and I hope it doesn't take us too long to figure out what is really happening.

Is useless drivel. Its a one page abstract that reads like a news media comentatry of the test. There are not even graphs of measurments taken, no specifics on the test setup. Nothing. Its not even Science by my definition. Lets move along, nothing to see here.

Can someone explain to me again why this couldn't be modified, scaled up and used as a micro thrust system for satellites and such?

First problem: it goes round and round, but doesn't produce net thrust in any one direction.

Second problem: it doesn't work in a vacuum. Those bulbs are partially evacuated - too much atmosphere, and it doesn't work, too little, and it doesn't work. Which points to this being some kind of expansion-contraction thermal effect rather than some kind of spacey photon-momentum thing.

Point of interest: I've also heard that if you put one of these things in a freezer you can get them to run backwards...

The Wired article speaks of Shawyer's EMDrive, which has been around for some time, and at first appears to confuse the EMDrive with a different technology Dr. Harold "Sonny" White of NASA has been working on for some time.

The tech report clears things up a bit. The test results are showing anomalous thrust, however NASA is reticent to attribute the thrust to Shawyer's theory of how it operates, which would violate conservation of momentum (hence the "impossible" in the title.

What the technical report says is something far more interesting. Dr. White has been working with several different test articles which use electromagnetic forces to increase the rate of virtual particle pair production in the quantum vacuum, then using the virtual particles during their very short time of existence as reaction mass. In other words, it is a reaction drive, but instead of carrying reaction mass in the tank, the investigators are trying to use mass borrowed from quantum vacuum plasma to generate a small, but measurable, amount of thrust.

The final sentence of the technical report contains the salient material:

"Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma. Future test plans include independent verification and validation at other test facilities."

attribute the thrust to Shawyer's theory of how it operates, which would violate conservation of momentumNo, it does not violate the law of conservation of momentum, why should it?Hint: http://en.wikipedia.org/wiki/E... [wikipedia.org]

Neither did Shawyer suggest the EM drive created virtual pairs, but the last sentence from the technical report says that since no known electromagnetic phenomenon can account for the observed thrust, the EM drive may be demonstrating "an interaction with the quantum vacuum virtual plasma". The quantum vacuum virtual plasma is the reference to vacuum fluctuation, or virtual particle/anti-particle pairs. If I understand the report correctly I believe he is suggesting that virtual particles may be providin

If it does work, it would eliminate the need for expendable fuel (just add electricity).

Always left out of these discussion is just how much electricity they need to produce useful thrust. While in theory, even a micro-Newton can eventually get you anywhere you want to go, practical considerations (E.G. the desire to not spend months in the Van Allen while spiraling outward, or the need to decelerate to enter planetary orbit) usually dictate a higher thrust level.

People often miss that the problem with ion drives and other electrical drives is that the exhaust velocity is too HIGH, not too low.

The higher the exhaust velocity, the more power you need for the same thrust. Making high specific impulse drives is easy - a microwave source can be ~80% efficient and has an exhaust velocity of the speed of light. The problem is that the power requirements are enormous.

Sure, energy from the sun is "free", but the mass of the solar cells to collect that energy is not free.

the vacuum is electrically neutral; the virtual charged particlescreated by quantum fluctuations will be in oppositely chargedpairs (e.g. electron / positron). Won't this drive send these pairsin opposite directions? So the whole thing will have zero thrust

this thought is the product of complete ignorance of how thisdrive is actually supposed to work however:)

I don't know the design, but couldn't you use the charge difference to separate them a bit, and then throw both away in the same direction? This seems implied by the comment that it violates conservation of momentum, because if the virtual pair then recombines momentum would seem to have disappeared.

A question is whether you could do this without using enough energy to stabilize the virtual pair as actual particles. It not then it would be extremely inefficient energetically.

Well, technically you are still using expendable fuel - it's just in the form of the hydrogen being fused in the core of the sun with the power being beamed away as omnidirectional EM radiation. That you're operating a power antenna rather than a on-site reactor, or that the available fuel supply is projected to last for billions of years are incidental to the physics.

Of course, for most practical purposes on a human timescale, operating within range of a nigh-infinite near-constant power broadcaster is in

For satellites, this is profound, as the life span of most satellites is determined by the amount of fuel they carry to correct orbital trajectories. Any time a satellite has to change orbit (i.e., retasked), it shortens it's service time significantly. Now, with reactionless propulsion, satellites are only limited by their ability to produce electricity. Of course, only when this technology proves out and it is able to be put into service.

For a Mars mission, for instance, it's a lot easier if all you need for propulsion is a fission reactor core and require no reactive fuel. Previously, you had to factor in this additional mass requirement. Now, all you have to worry about is breathable air and water for the crew.

Luckily, there are existing electric propulsion technologies. They don't provide much thrust, but they're extraordinarily efficient (they require so little "fuel" as to effectively not be using any, with VASIMR producing roughly 10x-20x the fuel efficiency of chemical rockets, and the current VASIMR engine is very inefficient in terms of heat loss and such). The problem is that we've never had any large source of power in space, so while electric propulsion is great for getting your probe around the solar system with a minimum of fuel consumption, or perhaps automated cargo runs to some future colony that isn't time sensitive, they're not going to get you anywhere.

However, if you fit a nuclear reactor inside a 747, strap a bunch of if VASIMR thrusters to it, then that'd actually work. You wouldn't get much thrust, though... the 200 kW VASIMR engine produces only 5N of thrust. If you put a nuclear reactor on the thing similar to what you'd find in a submarine, you'd get 300N of thrust. Compare that to the "Draco" rockets used by a SpaceX dragon as manoeuvring thrusters... they have 400N of thrust.

Still wrong. VASIMR ejects ionized particles--mass--which is the same problem as a chemical rocket: eventually you run out of shit to eject.

We're looking for a technology that can take energy and turn it into movement without ejecting any mass. In other words: We're looking to keep going even when we have no mass to eject. You can't eject the control units, the ship's body, its atmosphere, or its crew, if you want it to keep functioning or support life; so your nuclear pile might remain hot longer than your mass resources hold out.

I think your mass figures are off, that's above the maximum takeoff weight of a 747 (442mt), let alone the weight of the empty aircraft itself. Of course, somehow this 747 got into orbit, so the maximum takeoff weight is kind of meaningless.

An empty 747 weighs 178mt, and a submarine reactor weighs about 110mt. It's true that there are micro reactors that can produce about the same output at a fraction of the weight, but let's just say that we also need some radiators for cooling (since there's no active coo

Aside from the warp drive, which is currently from a physics stand point pure gobbledygook, the sub-luminal "impulse drive" of the Enterprise was a classical nuclear fusion plasma engine fueled by interstellar hydrogen gas (that's why those red things on the front of the Enterprise's warp drive nacelles were called Bussard [wikipedia.org] collectors). It is technologically speaking far in excess of what we can do today, but nonetheless theoretically permitted by known laws of physics.

The warp drive in Star Trek was based an earlier incarnation of this theory, which is based on results from Einstein. Warp drive FTL travel might not be possible, but the idea is definitely not "pure gobbledygook".

Physics says moving an object faster than light relative to spacetime is impossible. However, physics does not say the same about moving spacetime faster than light relative to a stationary object. Seems like the same thing, but they are very different in physics.
In fact inflation of the early universe was an expansion of spacetime itself, not the objects within spacetime moving apart, that occurred at speeds faster than light.

No, the best part is that NASA were able to prove 1000 times more accurately than the Chinese that the "engine" produced NO thrust and that there are some inaccuracies that they haven't eliminated.

...By arbitrarily ignoring the design used by not just the Chinese, but also the British, and coming up with their own entirely different and untested version. "Hah, we've proven that your Bugatti Veyron can't do 0-6 in under 2.5 seconds, because we tried it in our Ford Fiesta and it took over 9 seconds!".

You're right.
"Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not produce thrust. Specifically, one test article contained internal physical modifications that were designed to produce thrust, while the other did not (with the latter being referred to as the "null" test article)."
Also: "within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure"
I think maybe they made one of these:
htt [youtube.com]